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El Amal Project Field Trip
Cairo – Ain Soukhna Road
Bill Bosworth
November 21st
, 2015
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El Amal Project Field Trip
Cairo – Ain Soukhna Road
November 21st
, 2015
Field Trip Leaders: Dr. Bill Bosworth, Apache Egypt Companies
Sponsored by: Apache Egypt Companies
Overview
Northeastern Egypt underwent a complex
and interesting Phanerozoic geological his-
tory. In the area east of the city of Cairo
and reaching nearly to the Gulf of Suez,
most of the surface outcrops are comprised
of Eocene and younger strata. Field trips in
this region must therefore focus on late
Cenozoic sedimentation and deformation.
Some of the exposures are incredibly ro-
bust, and the area is crossed by paved
roads that make access very easy. Many
visitors would be amazed by how diverse
this geologic setting is, and by how much
can be learned about the greater context of
the geology of Egypt.
This field trip will stop at six very im-
portant outcrops along parts of both the
new and original Cairo – Ain Soukhna
road. We will examine the large-scale
structural setting, which was dominated by
compressional tectonics in the Late Eocene
(late Syrian Arc deformation) and then ex-
tensional tectonics in the Miocene (Gulf of
Suez rifting). This will bring us to out-
crops of the Middle and Late Eocene Ob-
servatory and Maadi Formations, overlain
by the Oligocene Gebel el Ahmar For-
mation and an unnamed but very important
Early Miocene section. We will observe
beautiful examples of siliciclastic fluvial
sandstones and conglomerates, large-scale
cross-bedding in carbonate platform strata,
basalt flows, major unconformities, minor
and major faulting, effects of diagenetic
silicification, and some very incredible
fossils.
Of utmost importance during the trip is
safety around the highways. We will be
stopping in locations where the buses can
be parked far removed from traffic lanes.
However, everyone must be extremely
careful any time they are walking to out-
crops any place near these roadways.
Please remain in the areas indicated by the
field trip leaders, and do not use mobile
phones while at the outcrop. The use of
phones will distract attention from presen-
tations and is unsafe while scrambling on
rocky surfaces. No hammers are necessary
and please do not try to remove the well-
preserved fossils we will see from the out-
crops.
This trip has been kindly sponsored by
Apache Egypt Companies which have a
long-standing commitment to supporting
students, educational institutions, and
training programs for young graduates
here in the host country of Egypt.
Stratigraphy
The stratigraphic column along the Cairo-
Ain Soukhna Road includes a thick section
of Eocene age shallow marine platform
carbonates deposited in an epeiric conti-
nental sea, overlain by Oligocene cross-
bedded and channelized fluvial sandstones
and conglomerates. These are then covered
locally by sub-alkaline basalt flows that
were erupted from fissures during the ini-
tiation of Miocene Gulf of Suez rifting.
The following brief description of these
stratigraphic units (Figure 1) is taken from
Klitzsch et al. (1987), Abd-Allah (1993),
and other references given at the end of
this field guide.
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Figure 1. Tectonostratigraphy of the field trip area. Sources of terminology are given in
the text. Absolute time scale is from Gradstein et al., 2012 (rounded to nearest Ma).
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Mokattam Formation (Group)
The Mokattam Formation was introduced
by Said (1962) from Gebel Mokattam,
near Cairo. Klitzsch et al. (1987) consider
the Mokattam to be of group status. It is
made up of white to yellow, nummulitic
limestones, dolomitic limestones, and
marls. The Mokattam Formation was con-
sidered Late Middle Eocene (Late Lute-
tian) by Cuvillier (1930b). The recent stud-
ies of Strougo (1979, 1985) indicate that it
is of Early to Middle Lutetian age.
The Mokattam Formation includes bio-
stromal limestone beds that are highly en-
riched in Nummulites gizehensis and
Nummulites midawarensis as well as Luci-
na mokattamensis, Wakullina (Huyella)
lefevrei, and corals. The thickness of this
formation as measured by Abd-Allah
(1993) is about 137 m.
Observatory Formation
The Observatory Formation was described
by Farag and Ismail (1959) from the ob-
servatory plateau, east of Helwan. This
formation consists of while to golden-tan
marly limestones with nodular limestones
at its top. Its age is Lutetian (Farag and
Ismail, 1959; Said, 1962; Strougo, 1985).
The Observatory Formation designates a
sequence of biogenic and bioclastic, fre-
quently cross-bedded, white limestones
and chalky limestones with some dolomit-
ic ledges in the middle and upper parts.
According to Abd-Allah (1993) it under-
lies the Qurn Formation and overlies the
Mokattam Formation.
The faunal content of the Observatory
Formation is characterized by the great
abundance of large miliolids, Febulerie
and Idalina, and imperforate conical
forams, Dictyoconus (Abd-Allah, 1993).
Other associated fossils include: Vulsella
crispata, Spondylus aegyptiacus, Wakulli-
na (Huyella) lefevrei, Lucina metableta,
Pterolucina monosulcata, Fimbria lamel-
losa, Fimbria kaitbeyensis, Anodontia in-
juriata, Barbatia (Rostarca) russeggeri,
Nucula (Lamellinucula) eymari, Mac-
rosolen uniradiatus, Fibularia luciani,
Echinocyamus blanckenhorni, Echino-
lampas africana, Echinolampas perrieri,
Orbitolites sp., corals and bryozoa.
The maximum thickness of the Observato-
ry Formation measured by Abd-Allah
(1993) at Gebel Akheider is about 203 m.
In general, the cross-bedding, corals, and
larger foraminifera belonging to the genera
Fabularia, Idalina and Dictyoconus in-
crease eastward, while the genus Nummu-
lites dominates in the west.
When bicycling or trekking through the
Wadi Digla Preserve the wadi floor and all
the massive cliff-forming section belong to
the Observatory Formation.
Maadi Formation
Klitzsch et al. (1987) refer to the Late Eo-
cene strata east of Cairo as the Maadi
Formation, first introduced by Said (1962).
The unit consists of grayish-green, highly
calcareous shale/mudstone and typically
dark-brown, highly argillaceous and are-
naceous limestone. The thickness of the
formation is about 70 m.
Abd-Allah (1993) divides these rocks into
three formations: Qurn, Wadi Garawi, and
Wadi Hof Formations. Strictly speaking, it
is probably not possible to map these for-
mations throughout the area and hence we
prefer the more general term Maadi For-
mation for our purposes.
Typical fossils of the Maadi Formation
include Nummulites contortus-striatus,
Nummulites fabiani, Nummulites incras-
satus, and Carolia placunoides. Numerous
other fossils are also listed by Abd-Allah
(1993). For the field geologist, one of the
most diagnostic features of the Maadi
Formation is the presence of extensive
oyster beds (e.g., ostrea clotbeyi, Ostrea
(Turkostrea) multicostata strictiplicata,
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Ostrea (Turkostrea) bogharensis) and the
general high abundance of fossil remains.
Gebel el Ahmar Formation
An unconformity separates the Upper Eo-
cene rocks from the Oligocene sediments
which were deposited in a fluviatile envi-
ronment (Said, 1962). The Oligocene
rocks often occur within fault-bounded
graben, or infill topography that existed at
the end of the Eocene. The unit consists of
varicolored, often unstratified, typically
cross-bedded and channelized sands, grav-
els, and chert-cobble conglomerates. Shuk-
ri (1954) called this the Gebel el Ahmar
Formation after exposures on the east side
of Cairo, many of which are now gone due
to extensive urban development. The
thickness is about 50 m but is extremely
variable.
The main fossils present in the Oligocene
strata are fossilized tree trunks which can
be up to 10 m in length. Fresh water snails
are also present.
Miocene Formations
The start of the Miocene Epoch is marked
by patchy eruptions of sub-alkaline basalts
and associated syn-depositional extension-
al faulting. These basalts have traditionally
been referred to as “Oligo-Miocene” in
age, based on general stratigraphic posi-
tion and K-Ar age dating (the K-Ar age
dates ranged from about 28 to 20 Ma
throughout the greater Cairo-Suez region).
New Ar40
/Ar39
dates, which are much
more reliable, show that all these basalts
(extrusive flows and dikes alike) were
produced at ~23 Ma – the Oligocene-
Miocene boundary – and within a very
short time period (Bosworth et al., 2015).
So any strata overlying the basalts, or con-
taining basalt detritus, are of Miocene age
(this would include the “upper Oligocene
unit” of Abd-Allah, 1993).
The rocks immediately overlying the bas-
alts, or laterally interfingering with them,
are basalt cobble conglomerates and highly
silicified sands. The basalt cobbles are
highly weathered, gray, and very friable.
They are not recycled through subsequent
erosion events.
In the eastern part of the Cairo-Ain Sou-
khna district most of the lower part of the
Miocene section consists of marine biotur-
bated marl, shale, sandstone and marly
limestone (Abd-Allah, 1993). The most
prominent fossils of this unit are bivalves
(Anadara diluvii, Glycymeris nummaria,
G. deshayesi, Spondylus cressicosta, Amu-
sium geneffensis, Chlamys holqeri, C.
submalvinae, Pecten ziziniae, P. cristato-
costatus, Hyotissa virleti, Crassostrea
gryphoides, Ostrea digitalina, Codakia
mediolaevis, Linga (Linga) columbella)
and echinoids (Psammechinus dubtus ,
Scutella zitieli , clypeaster istnmicus, En-
cope sp., Echinolampas amplus).
Abd-Allah (1993) assigned the age of this
assemblage, based chiefly on the pectinids
and the oysters, to the latest Early Miocene
(uppermost Burdigalian) to the Middle
Miocene (Langhian-Serravalian), which
agrees with the view of Sadek (1926).
Topping the marine strata is a non-marine
Miocene unit composed of massive chalky
sandstones and sandstones with gravel
bands. Sadek (1926) assigned this unit to
the Late Miocene. It is about 25 m thick.
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References
Abd-Allah, A.M.A. (1993) Structural ge-
ology of the area between El Galala El
Bahariya and Gebel Okheider. Ph.D.
Thesis, Ain Shams University, Cairo,
Egypt.
Bosworth, W., Stockli, D.F., and Helge-
son, D.E. (2015) Integrated outcrop,
3D seismic, and geochronologic inter-
pretation of Red Sea dike-related de-
formation in the Western Desert, Egypt
– the role of the 23 Ma Cairo “mini-
plume”. Journal of African Earth Sci-
ences, 109, 107-119.
Cuvillier, J. (1924) Contribution à l’étude
géologique du Mokattam. Bull Inst.
Egypte, 6, 93-102.
Cuvillier, J. (1930) Révision du nummuli-
tique Egyptien. Mem. Inst. Egypte, 16,
371 p.
Farag, I.A.M. and Ismail, M.M. (1959)
Contribution to the stratigraphy of the
Wadi Hof area (north-east of Helwan.
Bull. Fac. Sci., Cairo Univ., 34, 147-
168.
Gradstein, F.M., Ogg, J.G., and Hilgen,
F.J. (2012) On the geologic time scale.
Newsletters on Stratigraphy, 45, 171-
188.
Hermina, M., Klitzsch, E. and List, F.K.
(1989) Stratigraphic Lexicon and Ex-
planatory Notes to the Geological Map
of Egypt, 1:500,000 scale, Conoco
Inc., Cairo, Egypt, 263 p.
Klitzsch, E., List, F.K., Pöhlmann, G.
(1987) Geological Map of Egypt,
1:500,000 scale, Institut für An-
gewandte Geodäsie, Berlin, 20 sheets.
Moustafa, A.R. and Abd-Allah, A.M.
(1992) Transfer zones with en echelon
faulting a the northern end of the Suez
Rift. Tectonics, 11, 499-506.
Sadek, A. (1968) Stratigraphical and struc-
tural studies on the Cairo-Suez district.
Ph.D. Thesis, Cairo Univ., 275 p.
Sadek, H. (1926) The geography and geol-
ogy of the district between Gebel
Ataqa and El Galala El Bahariya (Gulf
of Suez). Geological Survey of Egypt,
120 p.
Said, R. (1962) The Geology of Egypt.
Elsevier, Amsterdam, 377 .
Shukri, N.M. (1954) On cylindrical struc-
tures and colouration of Gebel Ahmar
near Cairo, Egypt. Bull. Fac. Sci., Cai-
ro, Univ., 32, 1-23.
Strougo, A. (1979) The Middle Eocene –
Upper Eocene boundary in Egypt.
Ann. Geol. Survey Egypt, 9, 454-470.
Strougo, A. (1985) Eocene stratigraphy of
the eastern greater Cairo (Gebel Mo-
kattam-Helwan) area. Middle East Re-
search Center, Ain Shams University,
Sci. Res. Series, 5, 1-39.
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Figure 3. View of Middle Eocene roll into fault zone at Gebel Akheider (Stop 1).
Stop 1: Overview of Gebel Akheider looking west from turn-off on the Ain Soukhna Road
(Figure 3). Southward dip/roll into a fault zone is due to late Syrian Arc compression during
the Late Eocene.
Figure 4. Panorama of the Oligocene Gebel el Ahmar Formation roadcut (Stop 2).
Stop 2: Gebel el Ahmar Formation fluvial sandstone section (Figure 4). Well-developed cut
and fill structures, cross- and convolute bedding, small-scale sandstone deformation bands.
Group will sketch this outcrop.
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Figure 6. Cross-bedded Observatory Formation nummulitic limestones (Stop 3).
Stop 3: Observatory Formation cross-bedded and channelized platform carbonates (Figure 6).
Some beds contain abundant nummulites (large benthic foraminifera) and if re-worked can
form exploration targets in the subsurface.
Figure 7. Fault Zone Panorama in Maadi Formation (Stop 4).
Stop 4: Approximately east-west striking fault zone in Maadi Formation of complex litholog-
ic associations (Figure 7). Abundant fossils – please do not damage! Group will sketch this
outcrop.
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Figure 9. Google Earth satellite image of the NW-SE trending graben at Stop 5 and 6.
The light gray areas are mostly Middle Eocene Observatory Formation to the northeast
of the graben and Late Eocene Maadi Formation to the southwest of the graben. Si-
liciclastics are Gebel el Ahmar Formation except locally where they sit above the 23 Ma
basalts. Mapping is only preliminary and many of the smaller Oligocene exposures are
not indicated.
Stop 5: 23 ± 0.5 Ma basalt plug/flow within NW-SE trending graben (Figure 9). Dated by
Ar40
/Ar39
technique (Bosworth et al., 2015).
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Figure 10. Complexly faulted basalt-cobble conglomerate overlying Gebel el Ahmar
sandstone (Stop 6).
Stop 6: Complex faulting at the unconformity between the Oligocene Gebel el Ahmar se-
quence and the unnamed basalt cobble conglomerate above (Figure 10). Location is shown in
Figure 9.
